17.3 What are Catalysts and How Do They Affect ROR?

• What are catalysts?

  • increase rate of chemical reactions without being chemically changed at end of reaction
• Characteristics of catalysts:

  1. increases reaction rates but not yield
  2. not used up in reaction
  3. selective (only catalyse certain reactions)
  4. impurities can poison them
  5. physical appearance may change BUT chemically still the same
• Effect of catalyst on reaction rates:

  • catalysts provide an alternative pathway of lower Ea for reaction to occur - speeds up reaction
  • due to Ea : more reactant particles will have E >/= to Ea - increase frequency of effective collisions - increase ROR
• Industrial catalysts

  1. iron - manufacture of ammonia in haber process
  2. aluminium oxide/silicon dioxide - cracking of hydrocarbons
  3. nickel - manufacture of margarine from veg. oils
  4. platinum, palladium, rhodium - catalytic converters
• Characteristics of biological catalysts (enzymes):

  e.g. Digestive enzymes

  1. made of proteins
  2. temp-sensitive (at high temps - denatured - unable to catalyse)
  3. ph-sensitive
  4. have a specific catalytic action